Composite material reinforced by springlike metal structure

ABSTRACT

A composite material ( 16 ) comprising a polymer ( 17 ) as matrix and a metal structure ( 10 ) as a reinforcing element, characterized in that said metal structure ( 10 ) comprises two metal springs ( 12, 14 ), said springs ( 12, 14 ) being wound in opposite directions, said springs having coil parts which alternate with each other along the length of the metal structure, said springs being rolled so as to form a flat shape.

FIELD OF THE INVENTION

[0001] The present invention relates to a composite material whichcomprises a polymer as matrix and a metal structure as a reinforcingelement. The invention also relates to the use of such a compositematerial as reinforced canvass, sail cloth, cargo cover or tarpaulin.

BACKGROUND OF THE INVENTION

[0002] Composite materials with a polymer as a matrix and a metalstructure as a reinforcing element are known in the art. An example isWO-A-97/26146, which discloses a fabric of polyvinylchloride reinforcedby one elongated metal element such as a wire for use as reinforcementof canvasses.

[0003] The disadvantage of this structure is that a wire, in order toprovide the required strength and resistance against cutting and againstthe action of a pair of scissors, must have a diameter which issufficiently large. This large diameter wire then lacks flexibilitywhich may hinder or prevent the canvass from being folded.

[0004] WO-A-98/55682 solves the problem of flexibility by replacing thesingle steel wire by two or more steel cords in parallel adjacent toeach other. The steel cords have the advantage of providing sufficientflexibility while still providing the required strength. The increasedflexibility is obtained by using relatively thin filaments in the steelcords. However, in a number of safety applications such as canvasses,these thin filaments often lack the required resistance against theaction of a pair of scissors.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to avoid the drawbacksof the prior art.

[0006] It is a further object of the present invention to provide analternative metal reinforcement for polymer material in safetyapplications.

[0007] It is also an object of the present invention to provide a metalstructure which combines the properties of providing the requiredstrength and resistance against cutting and a sufficient flexibility.

[0008] It is still another object of the present invention to decreasethe weight of composite materials.

[0009] According to the invention there is provided a composite materialwhich comprises a polymer as matrix and a metal structure as areinforcing element. The metal structure comprises two metal springs.The springs are wound in opposite directions. The springs have coilparts which alternate with each other along the length of the metalstructure. The springs are rolled together so as to form a flat shapeand a coherent structure. During this process the individual wires aremore or less flattened, taking into account the tensile strength of thewires and the pressure exercised on the rolls.

[0010] This metal structure has following advantages:

[0011] (a) The metal structure is flexible in all directions.

[0012] (b) The metal structure provides an adequate resistance againstcutting and against the action of a pair of scissors since eachcross-section has at least three, but conveniently four separatecross-sections of metal wires.

[0013] (c) The metal structure has a great elastic springiness. Itallows to a large degree folding and bending without plasticdeformation.

[0014] (d) The metal structure is thin and flat in one direction, sothat a minimal amount of polymer is needed to cover it. This reduces theweight of the composite material.

[0015] A metal structure, as described hereabove, is known as such inthe art as corset bones for orthopedical applications.

[0016] The polymer is preferably a thermoplastic material such aspolyvinylchloride (PVC) which can be extruded around the metalstructure.

[0017] Other examples of suitable polymers include polyurethane andthermoplastic elastomers. The term thermoplastic elastomers refers toblends of polyolefins and rubbers in which blends the rubber phase isnot cured, blends of polyolefins and rubbers in which blends the rubberphase has been partially or fully cured by a vulcanization process toform thermoplastic vulcanizates, or unvulcanized block-copolymers orblends thereof.

[0018] The composite material can be in the form of a strip, a sheet ora fabric with a warp and a weft, where at least one of the warp or theweft are a strip.

[0019] The composite material can be used in applications where anincreased resistance against vandalism and robbery is desired. Examplesare the reinforcement of canvasses, sail cloths, tarpaulins, tentmaterial, cargo covers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will now be described into more detail withreference to the accompanying drawings wherein

[0021]FIG. 1 illustrates a metal structure used to reinforce a compositematerial according to the invention;

[0022]FIG. 2 illustrates a cross-section of a composite material in theform of a strip;

[0023]FIG. 3 illustrates a cross-section of a composite material in theform of a sheet;

[0024]FIG. 4 illustrates a composite material in the form of a fabric.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0025]FIG. 1 illustrates a metal structure 10 used to reinforce acomposite material according to the invention. The metal structure 10comprises two metal springs 12, 14 which are wound in oppositedirections. The springs 12, 14 are so wound in each other that a coilpart of spring 12 alternates with a coil part of spring 14, and viceversa. Thereafter the metal structure 10 is rolled so that it forms acoherent and flat structure. The rolling is so that the cross-sectionsof the individual springs 12 and 14 are also flattened. This flatteningincreases the resistance against the action of a pair of scissors.

[0026] The metal springs 12, 14 can be made of hard drawn steel wireswith following plain carbon composition: a carbon content between 0.06%and 1.10%, a silicon content between 0.10% and 0.40% and a manganesecontent between 0.20% and 1.20%.

[0027] Addition of micro-alloying such as chromium, vanadium, boron . .. is not excluded.

[0028] The use of stainless steel wires is neither excluded.

[0029] Typical values of the diameter d of the steel wires are 0.40 mmand 0.50 mm (in case of a non-round cross-section, the diameter d equalsto the diameter of a round cross-section with the same cross-sectionalsurface). Generally the wire diameter d ranges from 0.25 mm to 0.80 mm.

[0030] A typical value of the coil diameter D is 4.0 mm. Generally thecoil diameter D ranges from 3.0 mm to 6.0 mm after rolling.

[0031] The width W of the total metal structure 10 may vary betweenabout 4.0 mm and 11.0 mm after rolling.

[0032] The pitch p between two coils of the same spring wire variesbetween the value of a single wire diameter and several times the wirediameter.

[0033] The steel wire may be coated with a metallic coating such as zincor a zinc alloy (e.g. a zinc aluminum alloy with 2% to 10% Al and 0.1%to 0.4% of rare earth elements such as La and/or Ce) in order to providea good corrosion resistance.

[0034] Although the undulated and rough surface of the metal structurealready guarantees a good mechanical anchoring between the metalstructure 10 and the polymer matrix, the individual steel wires or thesteel structure as a whole may also be provided with a primer whichincreases the adhesion to the polymer matrix.

[0035] A first group of primers that can be used are thermosettingmaterials. Therefore binding agents are dissolved in an organic solventor are dispersed with a limited amount of a dispersing agent in water toform an emulsion or a suspension. Suitable binding agents are based onacrylate, alkyd/melamine, epoxy or phenol/epoxy resins. Other bindingagents giving a good adhesion to the metal and to the PVC compounds canalso be used. Additives such as anticorrosion pigments, wetting agentsand/or stabilizing agents can be added. The primer composition isapplied to the wires or to the metal structure by immersing the wires orthe structure into a solution, an emulsion or a suspension of the primermaterial. The primer composition can also be applied by spraying.

[0036] The thickness of the wet primer layer can be calibrated bypassing the wire and the primer through the calibrated opening of a die.The thickness of the primer layer can also be calibrated by felt wipingor by air wiping in a controlled air stream.

[0037] The thickness of the primer layer may be influenced by furtherdiluting the primer composition.

[0038] In order to allow drying and curing the wire or the metalstructure can be heated.

[0039] Since it is desirable that the weight of the composite is as lowas possible, the thickness of the primer layer must be low. Thethickness of the dry primer layer is preferably less than 10 μm, morepreferably less than 5 μm, for instance less than 1 μm. Radiationcurable resins such as ultra violet, electron beam or infra red curableresins are also suitable as primer.

[0040] A second group of primer layers that can be applied are hotmelts, for example ethylene copolymers such as EVA (ethyl vinylacetate), polyamides or polyesters. In order to obtain a sufficient thinlayer, it is preferred to use hot melts with a viscosity at 200° C. ofless than 20 Pa.s, more preferably this viscosity is less than 15 Pa.s.This hot melt can be applied with a variety of different equipment. Verysuitable is the melt pot. Also application by extrusion is possibleunder certain conditions. A method for the application by extrusion isdescribed in the patent specification BE 1006346.

[0041] Depending on the viscosity and the method of the application ofthe primer layer, primer layers with a thickness of less than 25 μm, forinstance less than 5 μm are obtained.

[0042] A third group are silane-compounds. These are bifunctionalmolecules: one functional group is responsible for the binding with themetal(oxides), the other functional group reacts with the polymer.

[0043] More details about these silane compound can be found in the PCTapplication with the application number WO-A-99/20682 (PCT/BE98/0015).Usually the silane compounds are diluted in alcohols, although they canbe diluted in other solvents or in water as well. With this type ofcompounds very thin primer layers with a thickness of 20 nm or even lesscan be achieved.

[0044]FIG. 2 shows a cross-section of a composite strip 16. Strip 16 hasa PVC matrix 17 which is extruded around a metal structure 10 which hasthree to four cross-sections of spring wires 12, 14. A typical width ofthe strip is 6.0 mm and a typical thickness 1.0 mm. Generally, both thewidth and the thickness depend upon the resp. width and thickness of themetal structure 10. The width may range from 3.0 mm to 25.0 mm and thethickness may range from 0.50 mm to 3.0 mm.

[0045]FIG. 3 illustrates a composite sheet 18 at least one direction ofwhich is reinforced by means of a metals structure 10.

[0046]FIG. 4 illustrates a fabric 20 where either the warp elements 16′or the weft elements 16″ or both are strips reinforced by means of ametal structure 10. Strips 16′ are welded to strips 16″ so that the PVCmaterial melts and functions as an adhesive between warp and weft.

[0047] The fabric 20 forms various meshes. The width M of the meshranges from 5.0 cm to 20.0 cm. Typical values are 15.0 cm×15.0 cm and10.0 cm×7.5 cm.

[0048] A fabric 20 may be used as reinforcement for canvasses by bondingor adhering the fabric at the interior side of the canvass so that theexternal side is still available for publicity or brand names.

[0049] Canvasses for trucks may be divided into two main categories:

[0050] canvasses of the curtain type and canvasses of the roll up type.

[0051] Canvasses of the curtain type are slidingly suspended onhorizontal rails and can be horizontally slid to one side to open thecanvass. Canvasses of the curtain type require flexibility in thehorizontal direction.

[0052] Canvasses of the roll up type can be rolled up vertically to openthe canvass. Canvasses of the roll up type require a flexibility in thevertical direction.

[0053] Fabrics 20 according to the invention may be realized so that forcanvasses of the roll-up type, the flexible metal structure 10reinforces at least the vertical strips 16′ and that for canvasses ofthe curtain type, the flexible metal structure 10 reinforces at leastthe horizontal strips 16″.

1. A composite material comprising a polymer as matrix and a metalstructure as a reinforcing element, characterized in that said metalstructure comprises two metal springs, said springs being wound inopposite directions, said springs having coil parts which alternate witheach other along the length of the metal structure, said springs beingrolled so as to form a flat shape.
 2. A composite material according toclaim 1 wherein said polymer is a thermoplastic material.
 3. A compositematerial according to claim 2 wherein said thermoplastic material ispolyvinylchloride.
 4. A composite material according to any one of thepreceding claims wherein said composite material has the form of astrip.
 5. A composite material according to any one of claims 1 to 3wherein said composite material has the form of a sheet.
 6. A fabriccomprising a warp and a weft which form meshes, said meshes having amaximum dimension ranging from 5 cm to 25 cm, at least one of the warpor the weft being formed by a strip according to claim
 4. 7. A canvassor a sail cloth, said canvass or sail cloth at least partiallyreinforced by a composite material according to any one of claims 1 to5.